📚 Year 9 Cambridge Economics Case Study: Sugar Tax in Practice | 九年级剑桥经济：糖税案例分析实战演练
This article takes you through a step-by-step case study of a sugar tax on soft drinks. You will learn how to apply demand and supply, elasticity, tax incidence and welfare analysis – exactly the skills needed for Year 9 Cambridge Economics. The case is set in an imaginary country, allowing you to practise structured evaluation just as you would in an exam.
这篇文章将带你一步一步地完成一个软饮料加征糖税的案例分析。你将学会如何应用需求与供给、弹性、税收归宿和福利分析——这些正是九年级剑桥经济课程所需的技能。案例设定在一个虚构的国家，让你能够像在考试中那样练习结构化的评估思路。
1. Case Study Scenario | 案例情景
Imagine a country called Sugarland, where sugary soft drinks are widely consumed. The government is worried about rising obesity and diabetes rates, so it decides to introduce a specific tax of $0.50 per litre on all sugar-sweetened beverages. You are asked to analyse the likely economic effects of this policy.
想象一个叫“甜糖国”的国家，含糖软饮料被大量消费。政府担心肥胖症和糖尿病发病率上升，因此决定对所有含糖饮料征收每升0.50美元的特殊税。你需要分析这项政策可能带来的经济影响。
Before the tax, the market for sugary drinks in Sugarland had an equilibrium price of $2.00 per litre and an equilibrium quantity of 10 million litres per month. Producers are mostly large bottling companies, and consumers range from young children to adults.
在征税前，甜糖国含糖饮料的市场均衡价格为每升2.00美元，均衡数量为每月1000万升。生产者主要是大型装瓶企业，消费者则涵盖从儿童到成人的各类人群。
2. Identifying the Economic Problem | 识别经济问题
The core economic problem here is market failure due to negative externalities. Sugary drinks cause health problems like obesity and tooth decay, which impose costs on society – for example, higher public healthcare spending. These external costs are not reflected in the free-market price, so too much is consumed.
这里的核心经济问题是负外部性导致的市场失灵。含糖饮料引发肥胖和蛀牙等健康问题，给社会带来了成本——例如公共卫生支出增加。这些外部成本并未反映在自由市场价格中，因此消费过度。
In addition, the government faces a policy trade-off: it wants to improve public health but must also consider the impact on businesses and consumers. The sugar tax is a government intervention aimed at correcting the market outcome.
此外，政府面临政策取舍：它希望改善公共健康，但也必须考虑对企业和消费者的影响。糖税正是一种旨在纠正市场结果的政府干预。
As a Cambridge Economics student, your job is to identify the stakeholders, apply relevant concepts and evaluate the policy’s effectiveness. Always start by naming the economic issue clearly.
作为剑桥经济学的学生，你的任务是识别利益相关者，应用相关概念并评估政策的有效性。请始终从清晰地说出经济问题开始。
3. Demand and Supply Analysis | 需求与供给分析
The sugar tax is a specific tax, meaning a fixed amount added to each litre sold. This increases the cost of production for bottling companies. In a demand and supply diagram, the supply curve shifts vertically upward by the full amount of the tax: $0.50.
糖税是一种从量税，即对每升售出的饮料加征固定金额。这增加了装瓶企业的生产成本。在需求与供给图中，供给曲线垂直上移全部税额：0.50美元。
Initially, the market equilibrium is at point E₀ (P=$ cts the demand curve D at a new equilibrium E₁. The price paid by consumers rises to, say, $2.30, and the price received by producers falls to $1.80. The quantity traded shrinks to 8 million litres.
最初，市场均衡在点E₀（P=2.00美元，Q=1000万升）。征税后，新的供给曲线S₁与需求曲线D交于新的均衡点E₁。消费者支付的价格上涨至例如2.30美元，生产者实际收到的价格下降至1.80美元。交易量缩减至每月800万升。
This simple analysis shows that a tax reduces quantity and splits the burden between buyers and sellers. The exact split depends on the price elasticity of demand and supply, which we examine next.
这一简单分析表明，税收减少了交易量，并由买卖双方共同分担。具体分担比例取决于需求价格弹性和供给价格弹性，我们接下来会分析这一点。
4. Price Elasticity of Demand | 需求价格弹性
Price elasticity of demand (PED) measures how responsive quantity demanded is to a change in price. It is calculated as:
需求价格弹性（PED）衡量需求量对价格变化的反应程度。其计算公式为：
PED = % change in quantity demanded ÷ % change in price
PED = 需求量变动的百分比 ÷ 价格变动的百分比
Sugary drinks in Sugarland are widely enjoyed and have relatively few close substitutes among teenagers; however, there are healthier alternatives like water and diet drinks. Surveys suggest that the demand is moderately elastic, with a PED of around -1.2.
甜糖国的含糖饮料深受喜爱，尤其在青少年中替代品较少；但也有水和无糖饮料等更健康的选择。调查显示需求具有中等弹性，PED约为-1.2。
A PED of -1.2 means that for any given price rise, quantity demanded falls by a larger percentage. This is significant for the tax: because demand is elastic, consumers are more likely to cut back their purchases when the tax pushes up the price. Thus, the tax is likely to reduce consumption quite effectively.
PED为-1.2意味着价格每上涨一定幅度，需求量的减少幅度会更大。这对税收意义重大：由于需求富有弹性，当税收推高价格时，消费者更可能减少购买。因此，该税在降低消费方面很可能相当有效。
5. Tax Incidence: Who Pays? | 税收归宿：谁来承担？
Tax incidence refers to how the burden of a tax is distributed between consumers and producers. With a specific tax, the consumer burden is the increase in price paid, and the producer burden is the fall in price received.
税收归宿是指税收负担如何在消费者与生产者之间分配。在从量税情况下，消费者负担是支付价格的上升部分，生产者负担是实际收入价格的下降部分。
When demand is more elastic than supply, producers bear a larger portion of the tax. In Sugarland, supply is relatively inelastic in the short run because bottling plants cannot easily switch production. Demand is elastic, so the producer burden is likely greater. From our earlier numbers: consumer price rose by $0.30, producer price fell by $0.20, thus consumers bear 60% of the tax, producers bear 40%.
当需求比供给更富有弹性时，生产者承担的税负比例更大。在甜糖国，短期供给相对缺乏弹性，因为装瓶企业不易转换生产线。而需求富有弹性，因此生产者负担很可能更重。根据前文的数字：消费者价格上升了0.30美元，生产者价格下降了0.20美元，因此消费者承担税收的60%，生产者承担40%。
This can be neatly summarised in a table:
这可以用一个表格清晰地概括：
| Stakeholder | Price Change | Share of Tax |
|---|---|---|
| Consumers | +$0.30 | 60% |
| Producers | -$0.20 | 40% |
Understanding tax incidence helps you go beyond the surface of a policy and discuss real-world effects – a mark-winning skill in Cambridge Economics.
理解税收归宿能帮助你深入政策表面，讨论现实世界的影响——这在剑桥经济学中是得分的关键技能。
6. Impact on Consumers | 对消费者的影响
The sugar tax makes sugary drinks more expensive, reducing consumers' real purchasing power. For low-income households, which spend a larger proportion of their income on such drinks, the tax is regressive – meaning it takes a bigger percentage of their income than it does from wealthier households.
糖税使含糖饮料变得更贵，降低了消费者的实际购买力。对低收入家庭而言，他们把收入中更大的比例花在这类饮料上，因此该税具有累退性——即相对于富裕家庭，税收占他们收入的比例更高。
Additionally, health-conscious consumers may switch to untaxed alternatives like diet drinks or water. This substitution effect improves public health but can also reduce the government's expected tax revenue if too many people switch.
此外，注重健康的消费者可能会转向无税替代品，如无糖饮料或白水。这种替代效应能改善公共健康，但如果太多人转向替代品，也可能减少政府预期的税收收入。
In the short run, some consumers may continue buying sugary drinks out of habit, but as price rises persist, they are likely to adjust their behaviour. The overall impact on consumer welfare is a loss in consumer surplus, shown by the area between the demand curve and the price line shrinking.
短期内，部分消费者可能因习惯而继续购买含糖饮料，但随着价格上涨持续，他们很可能会调整行为。对消费者福利的整体影响是消费者剩余的损失，表现为需求曲线与价格线之间的面积缩小。
7. Impact on Producers | 对生产者的影响
For producers, the tax increases production costs, squeezing their profit margins. Because the demand is elastic, they cannot pass on the full tax to consumers without losing a significant volume of sales. Some smaller firms may exit the market if they cannot reduce costs elsewhere.
对生产者而言，税收增加了生产成本，压缩了利润空间。由于需求富有弹性，他们无法将全部税收转嫁给消费者而不损失大量销量。一些无法从其他方面削减成本的小企业可能会退出市场。
Producers face a fall in producer surplus. The area above the supply curve and below the price received shrinks. In our example, the drop in quantity from 10m to 8m litres also means lower overall revenue for the industry, despite the higher price to consumers.
生产者面临着生产者剩余的下降。供给曲线以上、实际收入价格以下的面积缩小了。在我们的例子中，交易量从1000万升下降到800万升，这也意味着尽管消费者支付的价格更高，全行业的总收入却减少了。
Large multinational bottling companies may be better positioned to absorb the tax by innovating and reformulating products – for instance, reducing sugar content to escape the tax bracket. This adjustment is a dynamic response that can be discussed in a higher-level evaluation.
大型跨国装瓶公司则更有能力通过创新和重调配方来消化税收影响——例如降低含糖量以避开征税门槛。这种调整是一种动态反应，可在更高级别的评估中加以讨论。
8. Government Revenue and Externalities | 政府收入与外部性
The sugar tax raises government revenue: tax per unit multiplied by the new quantity sold. At $0.50 per litre and 8 million litres, the revenue is $4 million per month. This money can be hypothecated – used specifically to fund healthcare programmes or sports facilities for young people.
糖税增加了政府收入：每单位税额乘以新的销售量。按每升0.50美元和800万升计算，每月收入为400万美元。这笔钱可以专项用于资助医疗保健项目或青少年体育设施。
However, the tax is not intended primarily to raise revenue; its main goal is to reduce the negative externality. The external cost of consuming sugary drinks includes higher medical costs, lost productivity and poorer quality of life. When consumers pay a higher price that includes the tax, the market moves closer to the socially optimal level of consumption.
不过，该税的主要目标并非增加收入，而是减少负外部性。消费含糖饮料的外部成本包括更高的医疗费用、劳动生产力损失和生活质量下降。当消费者支付包含税收的更高价格时，市场消费水平会更接近社会最优水平。
If the tax exactly equals the marginal external cost at the optimal quantity, an effect called internalising the externality is achieved. In Sugarland, however, the tax is likely too low to fully offset the health costs, so some inefficiency remains – an important evaluation point.
如果税额恰好等于最优产量时的边际外部成本，便实现了所谓的外部性内部化。然而在甜糖国，税额很可能过低而无法完全抵消健康成本，因此仍存在一定低效率——这是一个重要的评估点。
9. Evaluation of the Sugar Tax | 评估糖税政策
Every good case study analysis finishes with a balanced evaluation. First, the advantages: the sugar tax directly targets the harmful good, reduces consumption, raises revenue for health projects and encourages producers to reformulate products. It is relatively simple to administer.
每一个好的案例分析都以平衡的评估收尾。先看优点：糖税直接针对有害商品，降低了消费，为健康项目筹集了资金，并鼓励生产者修改产品配方。它在管理上也相对简便。
On the other hand, the tax is regressive, hurting lower-income groups the most. It could lead to job losses in the soft drink industry. It also depends heavily on the price elasticity of demand – if demand becomes less elastic over time, the consumption reduction may fade. Furthermore, consumers may substitute to equally unhealthy non-taxed drinks.
另一方面，该税具有累退性，对低收入群体伤害最大。它可能导致软饮料行业的工作岗位流失。而且它在很大程度上依赖需求价格弹性——如果需求随时间推移变得缺乏弹性，消费的减少可能会减弱。此外，消费者可能转而消费同样不健康、但未被征税的饮料。
A strong conclusion acknowledges that no policy is perfect. The sugar tax can be part of a package, alongside public education and subsidies for healthy alternatives, to achieve a lasting improvement in public health.
一个有力的结论应承认，没有任何政策是完美的。糖税可以成为一揽子政策的一部分，与公共教育和健康替代品补贴相结合，来实现公共健康的持久改善。
10. Alternative Policies | 其他政策措施
Exam questions often ask you to consider alternative government interventions. To reduce sugary drink consumption, the government could also introduce a minimum price, impose an advertising ban aimed at children, or run awareness campaigns about sugar's health risks.
考试题目经常要求你考虑其他的政府干预措施。为减少含糖饮料的消费，政府也可以实行最低价格，禁止针对儿童的广告，或开展有关糖的健康风险的宣传活动。
A minimum price would set a legal floor above the equilibrium, but it could lead to excess supply and black markets. An advertising ban reduces information failure, but it is hard to enforce and may not change adult habits. A subsidy on healthy drinks like bottled water shifts demand, but it costs public money.
最低价格会设定一个高于均衡水平的法定价格下限，但它可能导致供给过剩和黑市。广告禁令能减少信息失灵，但难以执行，且可能不会改变成年人的习惯。对瓶装水等健康饮料发放补贴可以改变需求，但需要公共资金。
When comparing policies, use the criteria of effectiveness, cost, equity and ease of implementation. A well-reasoned comparison shows the examiner you can think critically like an economist.
在比较政策时，请运用有效性、成本、公平性和实施难易度等标准。合理的比较能向考官展示你可以像经济学家一样批判性地思考。
11. Exam Tips for Case Studies | 案例分析考试技巧
During a Cambridge Economics assessment, approach any case study with the same structure: define the problem, draw a relevant diagram, apply concepts like elasticity and externalities, discuss winners and losers, and always end with a justified evaluation.
在剑桥经济学的评估中，以同样的结构处理任何案例分析：界定问题，画出相关图表，应用弹性和外部性等概念，讨论赢家和输家，并始终以有理有据的评估结束。
Use precise economic vocabulary: 'market failure', 'incidence', 'regressive tax', 'internalise externality'. Support your analysis with data from the case, but avoid simply repeating numbers – explain what they mean.
使用准确的经济学词汇：“市场失灵”、“归宿”、“累退税”、“外部性内部化”。用案例中的数据支持你的分析，但不要只是重复数字——要解释它们的经济含义。
Diagrams do not need to be artistic, but they must be neatly labelled with axes, curves and equilibrium points. A correctly drawn demand and supply diagram with a tax shift can immediately earn you marks for application.
图表不需要精美，但必须整洁地标出坐标轴、曲线和均衡点。一张正确画出的需求与供给图，再配上税收引起的曲线移动，能让你立刻获得应用方面的分数。
Finally, manage your time. Allocate roughly one-third to reading and planning, half to writing analysis, and the remaining time to writing a concise evaluation. Practice makes this process automatic.
最后，管理好你的时间。大约分配三分之一的时间用于阅读和规划，一半用于撰写分析，剩余时间撰写简洁的评估。勤加练习会让这一过程变得信手拈来。
Published by TutorHao | Economics Revision Series | aleveler.com
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